Sleep and Low Power
The Astronode S has two sleep modes with some important differences between them:
- Sleep mode, which consumes a current of 4.4uA at room temperature (25°C).
- Deep-Sleep mode, which consumes a current of 320nA at room temperature (25°C).
Sleep mode
Sleep mode is used in the default configuration. The module will sleep when it is idle. It will automatically wake up and receive characters on the asset interface UART. The wakeup pin is not required in this mode because the module can wakeup in time to receive characters on the UART.
Sleep mode does not need the wakeup pin.
Deep-Sleep mode
Deep sleep mode can be enabled in the configuration register. This requires the use of the wakeup pin to wake the device before sending characters on the UART. In deep sleep, the module is in a very low power state and maintains the RTC, time of the last satellite contact, and ephemeris information. When it wakes up, the device is effectively starting up as if it was reset. This requires a 350ms delay between the wakeup pin going high and the first UART communication on the asset interface.
If the module enters deep sleep without saving the configuration, the previously saved configuration will be loaded when it wakes up. If no configuration has previously been saved the default configuration will be loaded. Note that if deep sleep is enabled but not saved, when the terminal wakes up, deep sleep may be disabled depending on the previously saved configuration. This has the important implication that if deep sleep mode is activated and the terminal is able to enter deep sleep, it will do so immediately, without saving the configuration to NVM. Be sure to set the wakeup pin high to complete a configuration save request/answer before the module enters deep sleep. With sleep mode (not deep sleep mode) unsaved configurations will persist in RAM.
Another important point is the module's use of sleep vs. deep sleep when payloads are queued. If there is a payload in the module's queue the module will not enter deep sleep, because it would lose the content of the RAM, which holds the queue. So the device will chose to use sleep mode if there is a message in the queue (including acked messages that have not been cleared by the asset yet). The user should not need to worry about this, but it could explain sleep current differences.
Deep sleep mode does need the wakeup pin to be set high 350ms before communicating on the asset interface UART.
It is possible to save deep sleep mode in the configuration without ever setting the wakeup pin.
Resolution:- Connect the wakeup pin to VDD.
- Set the configuration to use normal sleep mode and save.
Power Off
In some cases, it could make sense to power off the module completely. This would clear the RTC time, ephemeris information, and any payloads in the queue. When the module wakes up, it would be in a blind search mode. There are applications where this is the best option, and it will make more sense with a complete constellation.
Conclusion
Ultimately, use of sleep vs. deep sleep vs. power off depends on the use case.
| Mode | Sleep | Deep-Sleep | Power Off |
|---|---|---|---|
| Configuration | Default | N/A | |
| Power Consumption | 4.4uA | 320nA | 0A |
| UART Active | Yes | No | No |
| RTC | Maintained | Maintained | Reset |
| Ephemeris | Maintained | Maintained | Lost |
| Messages Queue | Maintained | Lost | Lost |
| Wake-up Pin | No | Required | No |
| Wake-up Delay | 8.5us | 350ms | 500ms |
- If the configuration is changed, it should be saved before entering deep sleep, otherwise the previously saved configuration will be used on wakeup. This save should be done with the wakeup pin active to ensure it doesn't go into deep sleep immediately after enabling deep sleep.
- If a payload is present in the module queue, the module will not enter deep sleep. It will use sleep mode instead. This is done automatically.
Older firmware releases may have slightly different wake-up delays. Refer to the appropriate datasheet if your Astronode S has a firmware version older than v2.7.0.
Downloads
Low Energy Guidelines (PDF), see Downloads.